The present invention relates to a calendar mechanism for timepieces, and more particularly to a calendar mechanism including an automatic correcting device for the varying lengths of month.
The conventional calendar mechanism of the watch comprises an annular date dial bearing the date indications, i.e. the dates from "1" to "31" one of which can be observed through the date window provided in the watch dial and a finger for driving the date dial. The date dial is provided with a toothing on the inner side thereof and the finger is secured on the date driving wheel which is adapted to be rotated one turn for every 24 hours. The finger is adapted to be brought into operative engagement with one of the teeth of the date dial during one complete revolution thereof to thereby index the date dial one step. In such a calendar watch, the date changes necessarily from date indication "30" to "31" irrespective of length of month. Accordingly, it is necessary to operate manually the date correcting device to drive the date dial from "31" to "1" at the end of the even month. In order to remove such trouble of manual operation, there has been provided an automatic correcting device which is adapted to index the date dial two days at night of 30th day of the even month to bring the indication "1" into the date window at the beginning of the next month.
The conventional automatic correcting device comprises a month disk provided with a cam on the periphery thereof and an auxiliary pawl pivotally mounted on the date dial which may be projected by the cam at the end of the even month for operative engagement with the finger on the date dial driving wheel, whereby the date dial may be indexed two days at the end of the even month. Such an automatic correcting device is not practical, because mechanism for actuating the auxiliary pawl by the cam is of complex construction and increases the thickness of the watch on the other hand resulting the smaller indication of month.